You may be looking for Makus III.

Magus III was the third planet in the Magus planetary system. This world had been visited by Guinan in or prior to 2367.

In that year, when REM sleep-deprived crewmembers aboard the USS Enterprise-D began to draft conspiracy theories about their inability to escape the Tyken's Rift in Ten Forward, Guinan was able to defuse the situation by firing an energy-beam rifle at the ceiling. She said she had acquired the weapon on Magus III. (TNG: "Night Terrors")